Multiplicity of Breeding Programs

A cultivar that is in perfect balance with one agro-ecosystem will be out of balance in another agro-ecosystem. This is because the epidemiological competence of various parasites differs markedly from one agro-ecosystem to another. In another agro-ecosystem, the previously balanced cultivar will become unbalanced. It will have too much horizontal resistance to some parasites, and too little to others. It follows that there should be a separate breeding program for each crop in each agro-ecosystem. Clearly, this will mean a multiplicity of breeding programs. It will also emphasise the importance of people in self-organisation. A multiplicity of breeding programs is possible only when there are many amateur breeding clubs made up of highly motivated individuals.

For our purposes, an agro-ecosystem is defined by the levels of epidemiological competence of the various crop parasites of economic significance. In practice, no attempt is made to measure these levels of epidemiological competence. All that is necessary is that the crop is bred and selected, using on-site selection, until it has an adequate level of horizontal resistance to all locally important parasites. No attempt need be made to measure these levels of horizontal resistance. All that matters is that the crop loss from parasitism is negligible in the absence of crop protection chemicals. And this resistance should be determined in farmer's fields, where there is no parasite interference and, eventually, no biological anarchy (see 7.16.1). It is the farmers themselves who will determine the boundaries of the agro-ecosystem, and the limits to the area of cultivation of a particular cultivar.

Some agro-ecosystems will prove to be quite large. One can envisage a single potato cultivar, for example, being valuable across a wide area of both Europe and North America, to say nothing of parts of South America, and Australia. But it will be of little value in areas where tropical parasites, such as bacterial wilt (Pseudomonas solanacearum), are epidemiologically competent. Equally, short-day tropical potato cultivars are useless in the long-day temperate regions.

In addition to environmental and pathosystem requirements, other factors must be taken into account. These might include the quality criteria of an export market, or the dietary preferences and/or cooking methods of the local people. In Mexico, for example, every region has its own dietary preference for the colour of beans (Phaseolus vulgaris), ranging from black, through the various colours of brown, red, pink, and yellow, to white.

Furthermore, each agro-ecosystem is likely to need a range of cultivars of each species of crop, with each cultivar providing special commercial or culinary properties. For example, potato cultivars can be classified into those that are best for salads, baking, boiling, roasting, mashing, and fries. There is plenty of work to be done. However, a single breeding club can easily operate several screening populations of one species of crop, covering several different agro-ecosystems and/or several different market requirements.

In practice, this multiplicity of breeding programs cannot possibly be achieved with institutional or corporate plant breeding. But is can be achieved very readily with myriads of plant breeding clubs. Most agro-ecosystems are likely to embrace some thousands of farmers, and such an agro-ecosystem can easily justify a fair number of breeding clubs.

A multiplicity of breeding programs will provide the enormous diversity needed for agro-evolution within each agro-ecosystem. But, because horizontal resistance is durable, a good cultivar need never be replaced, except with a better cultivar. So the progress will be irreversible.

Farmer selection and consumer selection will substitute for natural selection. This artificial selection will ensure a steady improvement in the balanced horizontal resistance, yield, quality of crop product, and agronomic suitability of new cultivars. Eventually, near-perfect cultivars will occur in every agro-ecosystem. This process might be termed 'agro-evolution'. It is, of course, micro-evolution, based on artificial selection, and the cultivars are agro-ecotypes (see 10.5).

After a few decades of intensive club activity, many cultivars will be available in each agro-ecosystem, with each cultivar being the best in its class. This agro-evolution cannot occur with the 'big space, high profile, short life' philosophy of institutional breeding based on vertical resistance and pedigree breeding. Indeed, it can be argued that the failure of twentieth century crop science has been a neglect of agro-evolution in favour of the over-control, over-simplification, and suboptimisation within institutional plant breeding.

One of the fundamental differences between pedigree breeding and agro-evolution is that pedigree breeding tends to look backwards to the parents. Evolution, on the other hand, is the exact opposite in that it looks forwards to the progeny. In natural evolution, the past is dead and gone forever, and the parents of the current generation are largely irrelevant. Evolution looks forwards. It is the fittest among the progeny that become the parents of the next generation, or that become new cultivars. In plant breeding, this forward-looking process is called recurrent mass selection.

The diversity of cultivars produced by this agro-evolution will also provide agro-ecosystem stability. An abnormal season, or the accidental introduction of a foreign parasite, might ruin a few cultivars, but it is unlikely to ruin all of them. This was seen, for example, when sugarcane smut (Ustilago scitaminea) reached Hawaii, where the 'melting pot' breeding had produced a wealth of alternative cane cultivars, many of which had high levels of horizontal resistance to this disease.

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